This invention relates to lighting and appliance panelboards which receive a plurality of overcurrent protective circuit breaker devices thereon. More specifically, this invention relates to structure on the panelboard and on a twin circuit breaker which cooperate to provide a proper installation or an indication of an obviously improper installation position for a twin circuit breaker on the panelboard.
As used herein throughout the specification and claims, a twin circuit breaker shall mean a device comprising two independent circuit breaker mechanisms and circuits contained within a unitary housing having a width equal to that of a related single pole circuit breaker. Twin circuit breakers afford a doubling of protected branch circuits within respective single pole mounting positions of a panelboard and are commonly used to provide additional circuits on an already full panelboard. There is a practical limit to the number of circuits that can be added to a panelboard determined by the designed ampacity of the panelboard current carrying members. Thus, although circuit breaker manufacturers provide doubling up capability through the use of twin breakers, it is necessary to limit the number of twin circuit breakers by limiting the positions on the panelboard at which such twin circuit breakers may be installed. When, as in the invention disclosed in this application, the means for indicating proper or improper installation positions for twin breakers is structurally embodied in the attachment of the circuit breaker to the panelboard rail, the structure should also accept previously offered single pole circuit breaker versions at the restricted locations.